The present invention relates generally to acoustic touchscreens and, more particularly, to a sealing system for use with acoustic wave touchscreens.
Touchscreens are used in conjunction with a variety of display types, including cathode ray tubes (i.e., CRTs) and liquid crystal display screens (i.e., LCD screens), as a means of inputting information into a data processing system. When placed over a display or integrated into a display, the touchscreen allows a user to select a displayed icon or element by touching the screen in a location corresponding to the desired icon or element. Touchscreens have become common place in a variety of different applications including, for example, point-of-sale systems, information kiosks, automated teller machines (i.e., ATMs), data entry systems, gaming machines, ticketing machines, etc.
A specific type of touchscreen, an acoustic touchscreen, has a touch-sensitive area on which the occurrence and location of a touch is sensed via the touch""s effect on acoustic waves propagating across the touchscreen surface. A common type of acoustic touchscreen employs Rayleigh waves (a term which, as used herein, subsumes quasi-Rayleigh waves). Illustrative disclosures relating to Rayleigh wave touchscreens include Adler, U.S. Pat. Nos. 4,642,423; 4,645,870; 4,700,176; 4,746,914; 4,791,416; and U.S. Pat. No. Re 33,151; Adler et al., U.S. Pat. Nos. 4,825,212; 4,859,996; and 4,880,665; Brenner et al., U.S. Pat. No. 4,644,100; Davis-Cannon et al., U.S. Pat. No. 5,739,479; and Kent, U.S. Pat. Nos. 5,708,461 and 5,854,450. Acoustic touchscreens employing other types of acoustic waves such as Lamb or shear waves, or combinations of different types of acoustic waves (including combinations involving Rayleigh waves) are also known, illustrative disclosures including Kent, U.S. Pat. Nos. 5,591,945 and 5,854,450; Knowles, U.S. Pat. Nos. 5,072,427; 5,162,618; 5,177,327; 5,243,148; 5,329,070; and 5,573,077; and Knowles et al., U.S. Pat. No. 5,260,521. The documents cited in this paragraph are incorporated herein by reference for all purposes.
Touchscreen applications may require that the touchscreen operate in an outdoor environment or in a relatively harsh indoor environment such as a factory or restaurant. Therefore the touchscreen may be subjected to rain, fog, wind, dust, cleaning solutions, sprays, liquid spills, etc. As a consequence of these conditions, typically some form of seal is required between the touchscreen and the system enclosure. Generally, however, it is difficult to achieve a satisfactory seal in an acoustic touchscreen due to the touch detection mechanism, i.e., surface propagating acoustic waves, as the seal may absorb an excessive amount of the acoustic energy, thereby compromising touchscreen performance. As a general rule, the acoustic loss attributable to the sealing system should be less than 6 dB.
U.S. Pat. No. 5,332,238 discloses a sealing system using a resilient, compressible foam strip that is substantially transmissive to surface acoustic wave energy. An acceptable level of attenuation is achieved by placing an open-cell surface against the touchscreen surface or by restricting seal contact to a corner of the foam strip. The foam strip also includes at least one membrane surface extending between the touchscreen and the housing which is impermeable to liquids. A structure for maintaining the foam strip in position is also disclosed.
An alternate sealing system is disclosed in U.S. Pat. No. 5,784,054. As disclosed, the seal is formed of a closed cell foam in which the touchscreen contacting surface is covered with a liquid impervious barrier. Alternatively, the seal may be formed of an expanded polymer such as expanded polytetrafluoroethylene. In at least one embodiment of the disclosed system, the seal is used in a CRT-based monitor without requiring replacement or modification of the normal housing or bezel.
What is needed in the art is a sealing system which provides a uniform compressive force along the perimeter of the seal and which can be used with a conventional CRT display device. The present invention provides such a sealing system.
The present invention provides a sealing system for use with acoustic touchscreens. The system includes a seal coupled to a frame, the frame being positioned directly over the acoustic touchscreen components, e.g., acoustic transducers, reflective arrays, etc. such that the seal prevents contamination of the underlying components. The system uses a plurality of tensioning elements that are either integral to, or separate from, the frame. The tensioning elements are preferably coupled at the four corners of the CRT, and more preferably coupled to the CRT mounting tabs. Assuming an approximately spherically curved touchscreen surface, the tensioning elements provide a uniform compressive force per unit length along the entire perimeter of the seal. As a consequence of the tensioning elements, the frame can be extremely thin, lightweight, and flexible, thus allowing it to substantially conform to the shape of the touch surface. Additionally, a very small and uniform gap can be maintained between the frame and the touch surface, e.g., less than 1 millimeter, thus allowing the designer to select from a wider range of sealing materials that meet the acoustic signal absorption requirements of the system while providing a robust contamination seal.
In one embodiment of the invention, the frame is fabricated from a single piece of plastic. Each of the four corners of the frame includes a channel or groove that is used to attach the frame to the CRT mounting tabs via retaining straps. Preferably this embodiment of the frame also includes a plurality of wiring channels for containing the transducer wires and corner cut-aways to allow transducer access. Although this embodiment is preferably used with a direct-on-tube acoustic touchscreen system, it can also be coupled to a display panel using an acoustic touchscreen overlay.
In another embodiment of the invention, a single piece frame is coupled to the CRT mounting tabs via outwardly spring-loaded fasteners, complimentary fasteners, bolts, or other fastening means that provide tension at the four corners of the frame. Corner cut-aways or access ports many be used to provide acoustic transducer access or the frame may cover and thus further protect the transducers.
In yet another embodiment of the invention, a retaining ring is fit around the body of the CRT. In one configuration the frame includes corner channels through which retaining straps are run. The retaining strap from each corner is coupled to the CRT retaining ring. Alternatively, tension straps may be positioned over the top surface of each side of the frame and attached at either end to the retaining ring.
In yet another embodiment of the invention, a frame is attached directly to an acoustic touchscreen overlay substrate. Preferably the frame is coupled to the overlay substrate using clips and tensioning cables.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.